Isolator--An Important Part of the Industrial Control Systems

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Summary

Isolator--also known as the signal isolator, is an important part of the industrial control system, is a linear optocoupler isolation principle, the input signal is converted to output. The input, output and working power three are isolated from each other, and are especially suitable for equipment instruments that require electrical isolation. In another words, an isolator is a mechanical switching device that, in the open position, allows for isolation of the input and output of a device. This pa[er is mainly talking some knowledge about isolator such as working principle fo isolator; its types; advantages; the differences between circuit breaker and isolator and etc.

Article core

isolator introduction

Installation way

guide rail installation

English name

isolator

Measurement accuracy

0.2%

Working temperature

0~50℃

Catagory

Semiconductor

Catalogs

Catalogs

I.Isolator Definition

IV.Isolator VS circuit breaker

5.2 Circuit power supply

II.solator Working and Principle

4.1 What is circuit breaker?

VI.The Advantage of Isolator

2.1 The reason of interference in the system

4.2 The differences between circuit break and isolator

VII.Technology Development

2.2 The solution to solve “ground loops”

V.The power supply modes of Isolator

III.Types of Isolator

5.1 Independent power supply

Introduction

I.Isolator Definition

Isolator--also known as the signal isolator, is an important part of the industrial control system, is a linear optocoupler isolation principle, the input signal is converted to output. The input, output and working power three are isolated from each other, and are especially suitable for equipment instruments that require electrical isolation. In another words, an isolator is a mechanical switching device that, in the open position, allows for isolation of the input and output of a device.

Chinese name

隔离器

Installation way

guide rail installation

English name

isolator

Measurement accuracy

0.2%

Working temperature

0~50℃

II.Isolator Working and Principle

2.1 The reason of interference in the system

Monitor and control the need to use all kinds of automation instrumentation and control system and actuator in the industrial production process, signal transmission between them is weak to the small signal, millivolt microampere, and tens of volts, or even thousands of volts, hundreds of amperes large signal; both low frequency DC signal, with high frequency pulse the signal system and so on, often found between the instrument and equipment of signal transmission interference, which makes the system unstable or misoperation. In addition to to the performance of the equipment itself causes each instrument, such as anti electromagnetic interference, there is a very important factor is due to the presence of potential difference between instruments and equipment between the signal reference point, thus forming the "ground loop" caused by signal transmission in the process of distortion. Therefore, in order to ensure the stable and reliable operation of the system, the problem of "grounding loop" is a problem that must be solved in the process of system signal processing.

2.2 The solution to solve “ground loops”

There are three solutions according to theory and practical analysis:

1)All site equipment grounding, make all the process loop only one ground, can not form a loop, this method appears to be simple, but in practice it is difficult to achieve, because some equipment requirements must be grounded in order to ensure the accuracy and ensure personal safety, some devices may because of the long-term corrosion and wear or by the effects of climate and the formation of new ground.

2)The electrical potential of the two junction is the same, but because the resistance of the grounding point is influenced by many factors such as geological conditions and climate change, such a scheme is not practical in practice.

3)In every process loop, the signal isolation method is used to break the process loop without affecting the normal transmission of the process signal, so as to thoroughly solve the grounding loop problem.

III.Types of Isolator

Isolator is a manually operated mechanical switch which separates a part of the electrical power. Isolators are used to open a circuit under no load. Its main purpose is to isolate one portion of the circuit from the other and is not intended to be opened while current is flowing in the line. Isolators are generally used on both ends of the breaker in order that repair or replacement of circuit breaker can be done without and danger. There are different types of isolators used for different applications such as single-break isolator, double-break isolator, bus isolator, line isolator, etc.

Constructional Features of Double Break Isolators

These have three stacks of post insulators as shown in the figure. The central post insulator carries a tubular or flat male contact which can be rotated horizontally with rotation of central post insulator. This rod type contact is also called moving contact. For voltages up to 145 KV system hand operated isolators are used whereas for higher voltage systems like 245 KV or 420 KV and above motorized isolators are used.

About the types of isolator,let's see a video:

This video shows the different types of isolator

Detail

IV.Isolator VS circuit breaker

In life we often see the circuit breaker and isolator word, the two is an important part of electric devices, but many people do not know what is their role, and even confuse the circuit breaker and isolator, they seem similar to their real name, its principles and effects are difference. Now let us to analyze the difference between circuit breaker and isolator.

4.1 What is circuit breaker

A circuit breaker is a switching device that can connect and split the current. Mainly to closing, carrying and breaking current when the circuit is normal, efficient allocation of electric energy; when the circuit is abnormal, such as short circuit, timely closing and breaking current, the protection of the electrical appliances, to ensure the safe operation of distribution network, is an important protection appliance.

4.2 The differences between circuit break and isolator

1)Differences in the principle of opening and breaking. The circuit breaker is a kind of mechanical switch appliance, and the isolator function is also a kind of switch. The difference is, circuit breakers and relays directly control the motor load, in general it amperage is relatively small, there are larger load control, but are generally used as intermediate relay and control circuit, the normal conditions and abnormal conditions can be connected, load breaking current, depending on the scope of its voltage can be divided into high voltage circuit breaker and low-voltage circuit breaker; while the isolator is having an isolation function, only the amperage is generally installed in the control cabinet front all load circuit breaker, play a whole on-off function.

2)The existence of Arc extinguishing function. The circuit breaker can extinguish the arc, and has a complete arc extinguishing system. The isolator does not have this function. The isolating switch usually does not have the arc extinguishing cover or the simple arc extinguishing cover in order to visualize the contacts. Therefore, the isolation switch can not be used to break off the electrified circuit, and it only plays a protective role in maintenance.

3)Different protection functions. The circuit breaker has a lot of protection functions, such as short circuit protection, over current protection, undervoltage protection, and so on. And burnt and the need to replace the fuse circuit breaker is different, generally do not need to replace parts in breaking fault current; isolator is transmission, conversion, isolation, transmission, operation of various industrial instrument signal, can protect the control loop of the lower interference suppression of unknown equipment, so as to improve the anti-interference of industrial production process ability to ensure the stability and reliability of the system.

V.The power supply modes of Isolator

There are three common power supply mode of isolator: independent power supply,circuit power supply and output circuit power supply.

5.1 Independent power supply

A DC power supply that needs to be equipped with an independent 20~35VDC. The advantage of this way is that the isolation transmission accuracy is high, the power supply, input and output are completely isolated, and the power supply of the multi-channel system does not need isolation, which ensures high anti-interference performance, and the input signal can be transformed into other types.

5.2 Circuit power supply

In the actual industrial monitoring system, the use of DCS, PLC or other display instruments with the internal power supply of the card is becoming more and more widely used. The circuit powered isolator often fails to meet the requirements of high precision of signal isolation transmission and high demand for power distribution of two wire transmitters. Therefore, the output circuit powered isolator not only preserves the superior performance of the independent power supply isolator, but also meets the requirements of the power supply interface of the output circuit.

Analysis

VI.The Advantage of Isolator

In the process of ground loops,In every process loop, signal isolation can be achieved by isolating card such as DCS or PLC, or with on-site isolated transmitter (partial device can be done), or signal isolator. In comparison, the use of signal isolators has the following advantages:

In most cases, the use of signal isolator and non isolation card is cheaper than that of isolating card.

The signal isolator is superior to the isolation card in isolation and electromagnetic interference.

The application of the signal isolator is flexible, and it also has the function of model conversion and signal distribution, and it is more convenient to use.

Signal isolators usually have single channel, dual channel, one access and two output channels. The channels are completely independent each other, which make the system configuration and routine maintenance more convenient.

About intelligent isolator: The SKGL type intelligent isolator can transform the input single or two way current or voltage signals to the isolated or single channel or two way linear current or voltage signals, and improve the electrical isolation performance of input, output and power supply.

VII.Technology Development

With the development of science and technology, the design of isolation terminals is becoming smaller and smaller, and the purpose of miniaturization is to take less space. Of course, user - intensive installation should be allowed, and dense installation has a heat dissipation problem, and internal power consumption must be reduced. Therefore,we also should pad attention to the value of internal power consumption.

There is another way ,transmitter and sensor are integrated and they must be placed at the designated sites. Generally, the isolation terminals are placed in the cabinet of the central control room, and the distribution terminals are sent to the field transmitter by the isolation terminals in the cabinet. Which one should be decided according to the PLC interface. Field debug may occur when the meter and PLC interface do not match. The sending device is four wire transmitter output 4 to 20mA, and the receiving port 4 to 20mA interface is a two wire loop power supply mode. If a direct connection is made, it will cause power conflict.

Circuit Breakers: A Technician s Guide to Low- and Medium-Voltage Circuit Breakers is a comprehensive overview of circuit breakers used in commercial, industrial, and utility applications and covers circuit breaker construction, operation, and maintenance. This new textbook covers insertion and removal (racking) of circuit breakers, safety and protection from arc-flash hazards, and troubleshooting procedures for circuit breakers.

--James R. White (Author)

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